Conventional systems for heating water and/or relatively small living spaces such as in a recreational vehicle generally fall into two classes of systems. The first class includes systems that have a heating element(s) that extend into a cavity which holds several gallons of water. That heating element ultimately heats the entire volume of water. Drawbacks to this first class include a lack of continuous hot water. In other words, if the entire tank containing several gallons of water is used, there is no longer hot water for the user and a period of time must elapse before hot water is available again. Because the entire volume of water must be heated by the heating element, it takes a relatively long time period to heat the water with such a system.
The second class of systems involves heating a relatively small volume of water with a gas or electric heating device. Conventional water heating systems for recreational vehicles in this class usually include a propane or other open-flame "flash furnace" heating system that directly heats the domestic eater. Open-flame systems like these are relatively expensive and relatively unsafe when used in a recreational vehicle. In addition, a propane heating system generally cannot provide a constant supply of hot water. Furthermore, the heating device adds to the complexity of the system and will wear and fail over time.